A variety of useful devices receive radiant energy in a first wavelength band and emit radiant energy in a different wavelength band. For example, periodically poled crystals, such as lithium niobate, are used to double the frequency of laser illumination and phosphors are deposited on the inside of cathode ray tubes to convert a stream of electrons into visible light.
One such wavelength converter is a phosphor color wheel that receives radiant energy and emits visible light. The phosphor color wheel is used to enable a solid state illuminator, such as a laser emitter, to replace the high pressure arc lamps traditionally used in projection displays. Solid state illuminators, such as light emitting diodes (LEDs) and laser emitters, have the potential to provide a very long lifetime and wider gamut compared to arc lamps.
Solid state illuminators, however, have drawbacks. The luminance, available flux within the etendue of a spatial light modulator (SLM), provided by an LED is limited, and high-power LEDs are difficult to cool in small packages. Laser sources have a very high luminance, but tend to create image speckle artifacts due to their extremely narrow bandwidth. Speckle artifacts are difficult and costly to eliminate in front projection display systems.
What is needed is low cost, efficient method of converting radiant energy from one wavelength band to another wavelength band in order to provide a long-life high-luminance illumination source that does not introduce any additional artifacts into the light beam.